OLED devices have begun to gradually replace cathode ray tube displays (CRTs) and liquid crystal displays (LCDs) in the marketplace. This is because OLED devices not only have a thinner profile, wider viewing angle, and less weight, but they also have faster response times and lower power consumption. Another advantage is the relatively simple structure of an OLED device, which typically includes an anode, a cathode, and an organic emission stack positioned therebetween. The simple structure permits the OLED device to be easily fabricated using relatively inexpensive manufacturing processes.
Referring to FIG. 3, a conventional OLED 10 includes a transparent substrate 11, an anode 12, an organic emission stack 19, and a cathode 18 arranged in that order from bottom to top. The organic emission stack 19 includes several layers depending on its functions. The organic emission stack 19 usually includes a hole injection layer 13, a hole transporting layer 14, an emitting layer 15, an electron transporting layer 16, and an electron injection layer 17 arranged in that order from the anode 12 to the cathode 18.
In operation, a positive electrical potential is applied between the anode 12 and the cathode 18. Holes from the anode 12 are injected into the emitting layer 15 through the hole injection layer 13 and the hole transporting layer 14. Electrons from the cathode are injected into the emitting layer 15 through the electron injection layer 17 and the electron transporting layer 16. Accordingly, light beams are generated from the emitting layer 15 as a result of hole-electron recombination within the emitting layer 15.
Generally, the anode 12 is made of a transparent conductive material with a high work function. For example, the anode 12 may be an indium tin oxide (ITO) layer. The hole injection layer 13 is made of organic material. However, a pure ITO layer has a hydrophilic property, and an organic layer has a lipophilic property. Because of these inconsistent properties, the anode 12 and the hole injection layer 13 cannot be combined together firmly. Furthermore, impurities, such as oxygen and water, are liable to be introduced between the anode 12 and hole injection layer 13. These impurities can greatly impair the operability of the OLED 10 and reduce the working lifetime of the OLED 10.
Accordingly, what is needed is an OLED and a method for fabricating the OLED which can overcome the above-described deficiencies.